Apparatus for continuously molding expandable synthetic resin, such as foam polyurethane, either rigid or flexible is well known and usually employs opposed endless belts that form a moving mold for confining and carrying the material as it foams and cures. These molds have a disadvantage of high initial cost and considerable power required to drive the belts that must necessarily be of heavy construction to resist the high foaming pressure. It is necessary to occasionally move the upper and lower belts away from each other for cleaning or repair, and accordingly the support for the upper belt is usually made so that the upper belt may be bodily moved. In view of the heavy and movable mounting for such rigid belt conveyors, it is difficult to control conditions within the mold, such as those of pressure and temperature.
Opposed belt conveyors have been used for:
1. The compression and adhesion of loose materials such as fibers, particles and crumbs into blocks and sheets. 2. The continuous molding of sheets and blocks of chemically produced materials such as urethane foam.
3. The lamination of skins to such blocks or sheets to produce panels with protective or decorative surfaces.
4. The direct production of laminated panels by combining such skins with the chemicals needed to produce the cellular core and restraining the expansion of the core to produce accurate and uniform thickness.
5. Restraining the rise of cellular products by conveying an open mold on a belt conveyor and utilizing a second belt to contact the top of the mold with enough pressure to resist the foaming pressure of the product.
In most cases there is a need for heat transfer either for warming or cooling the product as called for by the process. This is accomplished by controlling the temperature of the belt. This indirect means of applying or removing heat is very inefficient, has limitations of heat transfer and is not practical where both heating and cooling are required in separate zones of the process. Because of the pressures encountered it is necessary that the belt be of massive construction, resulting in high cost, high heating and cooling requirements and high power requirements for movement of the belt. The structure required for mounting such belts and their adjustment is also massive and expensive. Often the chemical reaction is so rapid that chemicals must be laid down adjacent to the nip of the two conveyors. This is very inconvenient for the operation of the chemical lay down equipment and the nipping itself is a safety hazard to operating personnel. Other problems which have been incurred are the rapid wear of the rollers needed to support the two belts against the product pressure and the low life expectancy of the bearings and other moving items when subjected to the high temperatures incurred in the process. Disassembly for cleaning and repair is also tedious.